eth/address: rename null address to zero address (#297)

* Adds support to check for the ethereum "null address"

* Many dreams have gone to the null address to die, this provides a
  simple check for developers to opt in to avoiding that fate.

* eth/address: rename null address to zero address

---------

Co-authored-by: Matt Rasband <[email protected]>

lib/eth/address.rb

@@ -17,7 +17,7 @@ module Eth
 
   # The {Eth::Address} class to handle checksummed Ethereum addresses.
   class Address
-    NULL = "0x0000000000000000000000000000000000000000"
+    ZERO = "0x0000000000000000000000000000000000000000"
 
     # Provides a special checksum error if EIP-55 is violated.
     class CheckSumError < StandardError; end
@@ -52,11 +52,11 @@ def valid?
       end
     end
 
-    # Checks that the address is the null address.
-    # 
-    # @return [Boolean] true if the address is the null address.
-    def null?
-      address == NULL
+    # Checks that the address is the zero address.
+    #
+    # @return [Boolean] true if the address is the zero address.
+    def zero?
+      address == ZERO
     end
 
     # Generate a checksummed address.

spec/eth/address_spec.rb

@@ -123,8 +123,8 @@
     end
   end
 
-  describe ".null?" do
-    let(:null) { Address::NULL }
+  describe ".zero?" do
+    let(:zero) { Address::ZERO }
     let(:addresses) do
       [
         "0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed",
@@ -134,13 +134,13 @@
       ]
     end
 
-    it "returns true for the null address" do
-      expect(Address.new(null)).to be_null
+    it "returns true for the zero address" do
+      expect(Address.new(zero)).to be_zero
     end
 
     it "returns false for a valid address" do
       addresses.each do |address|
-        expect(Address.new(address)).not_to be_null
+        expect(Address.new(address)).not_to be_zero
       end
     end
   end